1. Field of the Invention
The present invention relates to a method for machining workpieces on a cutting machine tool, in particular for drilling bores into workpieces, wherein a tool is put into rotation relative to the workpiece and the tool is moved relative to the workpiece with a feed motion, the tool executing an oscillating motion in the direction of the feed motion relative to the workpiece.
2. Related Prior Art
Such a method is known, for example, from DE 10 205 002 460 A1.
In chip-removing machining of workpieces, it is necessary that particular importance be attached to the clearance of chips, as well as to the accuracy and speed of machining In this case, not only do long chips produced during cutting give rise to problems with regard to disposal, but unwanted effects also occur during machining.
These problems occur in all machining operations in which chips are produced, i.e. in particular during drilling, milling and turning. Various measures are therefore taken to break the produced chips, so that they can be cleared more easily. Short chips offer not only handling advantages, however, as they are also desirable in respect of rapid and accurate machining and good surface condition.
In the making of deep drilled holes, in particular, the produced chips can result, for example, in jamming of the tool within the drilling hole, which can result in excessive wear on the tool and, consequently, in a reduction of the service life or even in breakage of the drill. Further, in this case, likewise, long chips impair the quality of the machined surface, since grooves can be produced.
Known from DE 31 39 540 A1, for the purpose of solving these problems, is the practice of cyclically withdrawing the drill from the bore during drilling and then advancing it again into the drilling hole, in order to clear the produced chips from the drilling hole. Withdrawal removes the drill from the chip, which therefore breaks the chips, and, owing to the shorter chip length, enables the chips to be taken away more easily. Upon being advanced again, the drill has to go back into engagement with the workpiece, which can result in quality problems, there also being the risk, in the case of rapid advancing, of the drill striking on the base of the drilling hole and breaking.
In DE 10 2005 002 460 A1 mentioned at the outset, in order to avoid these problems it is proposed that an oscillating motion, the stroke of which can be set and which goes to and fro in the axial direction, be superimposed on the continuous feed motion through mechanical measures. It is thereby intended that the produced chips become broken at an early stage, so as to produce short chips that are easily cleared and cause fewer problems in machining.
The known drilling appliance is therefore provided with an oscillator housing, the bearing bushing of which cooperates, via rolling elements, with a bearing bushing of an oscillator. Owing to the two bearing bushings, there is mechanically superimposed on the continuous feed motion, which in itself is unchanged, an oscillating motion whose oscillation stroke can be set within certain ranges through variation of the inclination of the bearing bushings in relation to one another.
The arrangement in this case is such that a complete oscillation stroke is executed during respectively two full revolutions of the drill. Thus, the frequency of oscillation is always half as great as the rotational speed of the drill. In the case of a feed motion of 0.02 mm per revolution of the drill, the oscillation stroke can be set to values below 0.02 mm.
In the case of this drilling mechanism, it is disadvantageous, in addition to its complicated and therefore cost-intensive and susceptible structure, that the manual setting of the oscillation stroke is difficult and time-consuming, and consequently less flexible. Further, owing to the fixedly predefined relationship between rotational speed and oscillation frequency, and to the fact that in each case the oscillation stroke must be fixedly set in advance for a machining operation, the known drilling mechanism does not fulfill all requirements. This applies, in particular, when machining is to be performed on workpieces of materials from which chips are not easily removed. It is therefore necessary for specially adapted drilling mechanisms to be used in each case for differing machining tasks.
It is known from DE 10 2006 015 038 A1 and DE 197 28 268 A1 to set a process parameter to a basic value and to vary the process parameter around this basic value when working a rotating workpiece with a tool. These known methods are not encountered with the problems associated with long chips and the respective removal thereof.